1. Field of the Invention
The invention relates to a System-on-a-Chip (SoC) test architecture, and more particularly to a test device for a hierarchical test architecture.
2. Description of the Related Art
System-on-a-Chip (SoC) devices are widely used today. With combining more and more different functions (cores) from different sources, the fault coverage of a core-based SoC device has been decreased dramatically. In order to reduce the test complexity of a SoC device, and for the purpose of test reuse, the IEEE (Institute of Electrical and Electrical and Electronic Engineers) has defined IEEE 1500 test standard, the test standard for core-based design.
FIG. 1 is showing the test wrapper defined by IEEE 1500.
Conforming to IEEE 1500 standard, a test wrapper 120 is wrapped around a core 110. The test wrapper 120 includes an N-bit wrapper instruction register (WIR) (not shown) for storing a test instruction, a 1-bit wrapper bypass register (WBY) (not shown), a wrapper boundary register (WBR) 130 for storing test data, a serial interface layer 140 and a set of standard wrapper serial control (WSC), wherein WIR and WBY are included in the serial interface layer 140. In addition, the test circuit can access data registers (DR) inside the core for testing the core. This type of data register is called a core data register (CDR).
In core-based design, another test standard, the IEEE 1149.1 standard can also be used, as shown in FIG. 2. The IEEE 1149.1 standard is designated for testing, and debugging a chip that is mounted on a printed-circuit board (PCB) and also for testing the interconnections between the chips that are mounted on the same PCB. Conforming to the IEEE 1149.1 standard, a core 210, a set of test access port (TAP) test signals (composed of TDI, TDO, TMS, TCK and optional TRST), a boundary-scan register (BSR, composed of serial linked boundary scan cells) 225 connected to input/output (I/O) ports 220 and an inner core 210, a user-defined data register (UDR) 230, an N-bit instruction register (IR) 240, a 1-bit bypass register 250, a TAP controller 260 and a multiplexer 270. The TAP controller 260 is composed of a finite state machine (FSM), a 4-bit state register and control circuits. FIG. 3 is a state diagram showing the FSM in the TAP controller 260, wherein all indicated states values are stored in the state register as the states of the state machine.
For the IEEE 1149.1 standard, data registers and corresponding test instructions other than the standard mandatory and optional instructions can be defined. By using the TAP controller, users can control testing processes and testing data path of an integrated circuit (IC). In addition to PCB testing, the IEEE 1149.1 standard can also be used to test and debug the inner cores of a SoC.
In addition, a core that is wrapped in a test wrapper conforming to the IEEE 1149.1 or IEEE 1500 standard may contain the other cores that are also wrapped in a test wrapper conforming to the IEEE 1149.1 or IEEE 1500 standard, the kind of test architecture may also be referred to as a hierarchical test architecture. In order to integrate the cores that are wrapped in the test wrappers conforming to the IEEE 1149.1 standard or IEEE 1500 standard and control the hierarchical test architecture, the present invention provides a test device and a method for a hierarchical test architecture.